Abstract
AbstractMicrometer‐scale maps of authigenic microstructures in submarine basaltic tuff from a 1979 Surtsey volcano, Iceland, drill core acquired 15 years after eruptions terminated describe the initial alteration of oceanic basalt in a low‐temperature hydrothermal system. An integrative investigative approach uses synchrotron source X‐ray microdiffraction, microfluoresence, micro‐computed tomography, and scanning transmission electron microscopy coupled with Raman spectroscopy to create finely resolved spatial frameworks that record a continuum of alteration in glass and olivine. Microanalytical maps of vesicular and fractured lapilli in specimens from 157.1‐, 137.9‐, and 102.6‐m depths and borehole temperatures of 83, 93.9, and 141.3 °C measured in 1980, respectively, describe the production of nanocrystalline clay mineral, zeolites, and Al‐tobermorite in diverse microenvironments. Irregular alteration fronts at 157.1‐m depth resemble microchannels associated with biological activity in older basalts. By contrast, linear microstructures with little resemblance to previously described alteration features have nanocrystalline clay mineral (nontronite) and zeolite (amicite) texture. The crystallographic preferred orientation rotates around an axis parallel to the linear feature. Raman spectra indicating degraded and poorly ordered carbonaceous matter of possible biological origin are associated with nanocrystalline clay mineral in a crystallographically oriented linear microstructure in altered olivine at 102.6 m and with subcircular nanoscale cavities in altered glass at 137.9‐m depth. Although evidence for biotic processes is inconclusive, the integrated analyses describe the complex organization of previously unrecognized mineral texture in very young basalt. They provide a foundational mineralogical reference for longitudinal, time‐lapse characterizations of palagonitized basalt in oceanic environments.
Highlights
The alteration of basaltic rock is a fundamental mineralogical process that has influenced the chemical and material properties of Earth's oceanic and continental crust for four billion years
Multiple high‐resolution microanalyses have been applied to three specimens of submarine basalt drill core collected in 1979 from Surtsey volcano, 15 years after eruptions terminated
The resulting micrometer‐scale maps build on previous investigations of the drill core samples (Jakobsson & Moore, 1982, 1986)
Summary
The alteration of basaltic rock is a fundamental mineralogical process that has influenced the chemical and material properties of Earth's oceanic and continental crust for four billion years. An isolated oceanic island created from 1963–1967 in the offshore extension of Iceland's southeast rift zone, provides an extremely well‐constrained record of the initial stages of these alteration processes in a Geochemistry, Geophysics, Geosystems hydrothermal system that traverses submarine and subaerial basaltic tephra, tuff, and minor intrusions (Thórarinsson, 1967; Jakobsson, 1978; Jakobsson & Moore, 1982, 1986; Figure 1). A hydrothermal anomaly, in which a maximum borehole fluid temperature, 141.3 °C measured in 1980, occurred at 100‐ to 106‐m depth below surface (Figure 1), is thought to be a convective system that developed in response to basaltic intrusions that fed lava flows from 1964–1967 (Jakobsson, 1978; Jakobsson & Moore, 1982; Stéfansson et al, 1985). The International Continental Scientific Drilling Program SUSTAIN project (Jackson et al, 2015) drilled three new cored boreholes through the still hot volcano in 2017 (Jackson et al, 2019)
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